1. Field of the Invention
The present invention relates to a method for producing a semiconductor laser device with a reflection protective film formed on a light-emitting facet thereof, used for an optical pickup or the like in an apparatus such as a CD player and an MD player, and an apparatus for producing the same.
2. Description of the Related Art
In recent years, semiconductor laser devices used for optical pickups of CD players and MD players are in increasing demand. In particular, highly reliable semiconductor laser devices with less variations in lasing characteristics have been demanded. In order to supply such good quality semiconductor laser devices at a low cost, they are required to be mass-produced with a high yield.
Conventionally, in a practical semiconductor laser device, a single thin film made of silicon nitride, alumina, silicon, or Al.sub.x Ga.sub.1-x As crystal is formed, or these thin films are layered, on a light-emitting facet, whereby a reflection protective film is formed so as to adjust the reflectance of the light-emitting facet to a desired value. Such a reflection protective film improves lasing characteristics such as a threshold current for laser oscillation, and prevents the light-emitting facet from degrading or being damaged, thereby ensuring the reliability of the semiconductor laser device for a long period of time. (In this application, such a film which has functions of adjusting the reflectance of the light-emitting facet as well as protecting the light-emitting facet is called the "reflection protective film".) However, it is difficult to form a desired reflection protective film on a semiconductor wafer because the reflection protective film is required to be formed on a facet of each semiconductor laser device.
A method for forming the above-mentioned reflection protective film is disclosed, for example, in Japanese Laid-Open Patent Publication No. 6-296059. According to this method, as shown in FIGS. 5A and 5B, a wafer is cleaved to form a plurality of bar wafers 1 having a predetermined cavity length. The bar wafers 1 are inserted into a groove 3 of a jig 2 in the thickness direction so as to be fixed in the jig 2. At this time, partitioning members 4 are inserted between the respective bar wafers 1 so that the bar wafers 1 do not come into contact with each other. Thereafter, a reflection protective film is formed on each light-emitting facet 5 (cleavage facet) of the bar wafers 1 exposed from the jig 2.
According to the above-mentioned conventional method, it takes a long time to fix the bar wafers 1 in the jig 2 by inserting them into the groove 3 thereof, and automation of the inserting process is very difficult to achieve. Furthermore, the bar wafers 1 are actually inserted into the groove 3 by holding side surfaces, i.e., the light-emitting facets 5 thereof, with a pincette, which may damage the light-emitting facets 5. The bar wafers 1 may also be broken when being fixed in the jig 2. When gaps are present between the bar wafers 1 and the partitioning members 4 when fixed in the jig 2, there is a possibility that the reflection protective film adheres to electrodes formed on the top and bottom surfaces of the bar wafers 1 as well as the light-emitting facets 5. These factors make it difficult to improve the production yield of this method.
A method for forming a reflection protective film on respective facets after a wafer is cleaved to individual semiconductor laser devices (chips) is disclosed in, for example, "Cost Reduction of Semiconductor Laser" H. Matagi, Optics, Vol. 24, No. 5, pp. 295-296 (May, 1995). According to this method, as shown in FIG. 6, a semi-conductor laser chip 11 is die-bonded to a stem 12, having three leads 16, 17, and 18, via a heat sink 13 and a submount 14. A PIN photodiode (PIN-PD) 15 is mounted on the stem 12. The stem 12 is introduced into a protective film forming machine one by one after the semiconductor laser chip 11 is connected to the lead 16 and the PIN-PD 15 is wire-bonded to the lead 18, whereby a reflection protective film is formed on a facet of the semiconductor laser chip 11.
In the above-mentioned conventional method, the reflection protective film is formed on each facet of the semiconductor laser chips 11 after being cleaved from a wafer and die-bonded to the stem 12. Therefore, die-bonding and wire-bonding are conducted between the step of cleaving a wafer to the individual semiconductor laser chips 11 and the step of forming the reflection protective film on each facet of the semiconductor laser chips 11. During this period, undesired phenomena such as the damage of a light-emitting facet and the formation of an unwanted oxide layer on the light-emitting facet are likely to occur, causing the malfunction and decrease in reliability of the semiconductor laser chips 11. Furthermore, since the formation process of the reflection protective films are successively conducted with respect to the individual stems 12 provided with the semiconductor laser chips 11, a very large apparatus is required for simultaneously forming the reflection protective films on the facets of a number of semiconductor laser chips 11. This contributes to the prevention of mass production and cost reduction.